I am constantly wrestling with this same alligator. My wife and I have been together one way or another for over 30 years. From day one she knew I had gender issues. She was even OK with my sort of monthly escapes from maleness cross-dressing days. Eventually even staying around the house when I did. Everything was cool because I was just a cross-dresser. No thoughts of transitioning. Been there, tried it twice, wasn't for me. Well, that was 30 years ago. Dropping the T-Bomb on her 6 years ago was not easy, nor did she take kindly towards it. But we got through it. Plenty of honest and open communications.
One great characteristic we both share is that neither of us wants to stand in the way of the others happiness. During my many "WTF am I Doing

" meltdowns when I said I want to stop this craziness she was my reality therapist. During her meltdowns when I offered to stop she said NFW.
My wife has and does say "I did not marry a woman. I like men. I like what they have. I like how they make me feel". Since I started down this path I've grown immensely as a person. Being back on HRT has also helped plenty. Our love is perhaps the strongest it has ever been. Yet now I also hear "I cannot think of you as a husband with those bumps on your chest" Or, "I'm afraid of freaking out over your boobs if we tried having sex". Before HRT she often took advantage of how aroused playing with them was for me!
When the rubber of reality meets the road of transition....
My therapist and my wife like to point out that I am not God or some soothsayer. I cannot accurately predict, much less have control over the future. I know I like have all the angles covered before doing something. It's a personal trait and an occupational hazard for me. If, or when, I make a transition, I'd sure like to know how it will mostly play out even before doing it. That will never be.
One day at a time. You may grow closer, or apart. Or both. My wife and I long ago before we actually committed to government paperwork our relationship, we agreed that if the other wanted, or needed, to have sex with someone else it would be OK provided the rules are followed. To date neither of us exercised that option. That option has also been mentioned far more these past 6 years than the previous 30.
When faced with difficult questions or choices, I found that the answer to one simple question always yields the answer. "Which Pain is Worse?"